Phase modulation active device, method of driving the same, and optical apparatus including the phase modulation active device

ABSTRACT

A phase modulation active device and a method of driving the same are provided. The method may include configuring, for the phase modulation active device including a plurality of channels that modulate a phase of incident light, a phase profile indicating a phase modulation target value to be implemented by the phase modulation active device; setting a phase limit value of the phase modulation active device; generating a modified phase profile based on the phase profile by modifying the phase modulation target value, for at least one channel from the plurality of channels that meets or exceeds the phase limit value, to a modified phase modulation target value that is less than the phase limit value in the phase profile; and operating the phase modulation active device based on the modified phase profile. Thus, improved optical modulation performance may be achieved.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.15/685,314, filed Aug. 24, 2017, which claims priority from KoreanPatent Application No. 10-2016-0107777, filed on Aug. 24, 2016 in theKorean Intellectual Property Office, the disclosure of which isincorporated herein in its entirety by reference.

BACKGROUND 1. Field

The present disclosure relates to a phase modulation active device, amethod of driving the same, and an optical apparatus including the phasemodulation active device.

2. Description of the Related Art

An optical device for changing transmission/reflection, polarization,phase, strength, path, etc., of incident light is used in variousoptical apparatuses. To control the aforementioned characteristics in adesired manner in an optical system, optical modulators having variousstructures have been suggested.

For example, liquid crystal having optical anisotropy, amicroelectromechanical system (MEMS) structure using fine mechanicalmovement of a light blocking/reflecting element, and so forth have beenwidely used for general optical modulators. These optical modulatorshave a slow operation response time of several microseconds or more dueto characteristics of a manner of operation thereof.

Recently, there has been an attempt to apply a meta structure to anoptical modulator. The meta structure is a structure in which a valuesmaller than a wavelength of incident light is applied to a thickness, apattern, or a period. By combining phase modulation types with respectto incident light, optical modulation may be implemented in variousforms and various optical characteristics may be achieved with highresponse speed, and may be favorably applied to ultra-micro devices.

SUMMARY

The present disclosure provides a phase modulation active device, whichis capable of implementing desired optical capabilities by combiningphase modulation types, and a method of driving the phase modulationactive device.

Additional aspects will be set forth in part in the description whichfollows and, in part, will be apparent from the description, or may belearned by practice of the presented example embodiments.

According to an aspect of an example embodiment, a method of driving aphase modulation active device may include configuring, for the phasemodulation active device including a plurality of channels that modulatea phase of incident light, a phase profile indicating a phase modulationtarget value to be implemented by the phase modulation active device;setting a phase limit value of the phase modulation active device;generating a modified phase profile based on the phase profile bymodifying the phase modulation target value, for at least one channelfrom the plurality of channels that meets or exceeds the phase limitvalue, to a modified phase modulation target value that is less than thephase limit value in the phase profile; and driving the phase modulationactive device based on the modified phase profile.

The setting the phase limit value may include obtaining a correlationbetween a phase modulation value of one of the plurality of channels anda voltage applied to the phase modulation active device; and, based onthe correlation, setting a value at which a phase change is saturated asthe phase limit value.

The setting the phase limit value may further include setting a minimumvalue and a maximum value of phase modulation to be implemented by thephase modulation active device based on the correlation.

The maximum value may be less than or equal to the phase limit value andmay be greater than 90% of the phase limit value.

The modifying the phase modulation target value may include modifyingthe phase modulation target value, for the at least one channel of theplurality of channels that meets or exceeds the phase limit value, tothe minimum value.

The modifying the phase modulation target value may include modifying afirst phase modulation target value, for a first portion of channelsfrom the plurality of channels that meet or exceed the phase limitvalue, to the maximum value, and modifying a second phase modulationtarget value, for a second portion of the channels from the plurality ofchannels that meet or exceed the phase limit value, to the minimumvalue.

The second phase modulation target value for the second portion ofchannels may be set to the minimum value when the second phasemodulation target value is higher than a predetermined threshold value.

The setting the phase limit value may further include setting voltagevalues V₀ and V_(m) to be applied to the phase modulation active device,the voltage values V₀ and V_(m) corresponding to the minimum value andthe maximum value, respectively.

The driving the phase modulation active device may include applying thevoltage value V_(m) to a first portion of channels from the plurality ofchannels that meet or exceed the phase limit value, and applying thevoltage value V₀ to a second portion of the channels that meet or exceedthe phase limit value.

According to an aspect of an example embodiment, there is provided aphase modulation active device that may include a phase modulatorincluding a plurality of channels, each channel of the plurality ofchannels configured to modulate a phase of incident light independentlyfrom other channels of the plurality of channels, a signal input unitconfigured to apply a first input signal for phase modulation to theeach channel of the plurality of channels; a signal input unitconfigured to apply a first input signal for phase modulation to theeach channel of the plurality of channels; and a controller configuredto control the signal input unit to apply the first input signal, whichimplements a phase modulation value less than a target phase modulationvalue of a channel, to at least one channel among the plurality ofchannels that exhibits a phase limit.

The phase modulation value less than the target phase modulation valuemay be a minimum value among phase modulation values that areimplemented by the phase modulator based on the first input signal.

A phase limit value may be less than 330°.

A second input signal, which implements a maximum value among the phasemodulation values that are implemented by the phase modulator based onthe second input signal, may be applied to at least one other channelamong the plurality of channels that exhibits the phase limit.

The second input signal that implements the maximum value is applied toa first portion of channels that exhibit the phase limit, and the firstinput signal that implements the minimum value may be applied to asecond portion of the channels that exhibit the phase limit.

The first input signal may be applied to second portion of the channelshaving target phase values that exceed a predetermined threshold value.

The phase modulator may be configured to modulate the phase of theincident light according to an applied voltage, and from among thechannels that exhibit the phase limit, a first voltage valueimplementing the minimum value may be applied to the second portion ofthe channels having target phase values exceeding a predeterminedthreshold value, and a second voltage value implementing the maximumvalue may be applied to the first portion of the channels.

The phase modulator may include an active layer having opticalcharacteristics that change with an electric signal, a nano array layerincluding a plurality of nano structures arranged over the active layer,and an electrode layer configured to apply a signal to the active layer.

Each nano structure of the plurality of nano structures may have a shapedimension that is smaller than a wavelength of the incident light.

Each nano structure of the plurality of nano structures may include ametallic material.

The phase modulator may further include an insulating layer disposedbetween the nano array layer and the active layer.

The signal input unit may be configured to apply a voltage between eachnano structure of the plurality of nano structures and the electrodelayer.

Each nano structure of the plurality of nano structures may include adielectric material.

The phase modulator may further include a conductive layer disposedbetween the nano array layer and the active layer. The signal input unitmay be further configured to apply a voltage between the conductivelayer and the electrode layer.

The signal input unit may be further configured to cause the phasemodulator to perform at least one of beam steering, focusing,defocusing, beam shaping, or beam splitting.

According to another aspect of the present disclosure, there is providedan optical device including the phase modulation active device describedabove.

According to an aspect of an example embodiment, there is provided alidar device that may include a light source unit, a phase modulationactive device and a sensor unit. The phase modulation active device maybe configured to steer light from the light source unit toward anobject. The phase modulation active device may include a phase modulatorincluding a plurality of channels, each channel of the plurality ofchannels configured to modulate a phase of incident light independentlyfrom other channels of the plurality of channels; a signal input unitconfigured to apply an input signal for phase modulation to the eachchannel of the plurality of channels; and a controller configured tocontrol the signal input unit to apply the input signal, whichimplements a phase modulation value less than a target phase modulationvalue of a channel, to at least one channel among the plurality ofchannels that exhibits phase limit. The sensor unit may be configured toreceive the light that is steered by the phase modulation active device,irradiated to the object, and reflected from the object.

The controller may be further configured to control the signal inputunit to sequentially adjust a steering direction of the phase modulationactive device to scan the object.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects will become apparent and more readilyappreciated from the following description of the example embodiments,taken in conjunction with the accompanying drawings in which:

FIG. 1 is a block diagram schematically illustrating a structure of aphase modulation active device according to an example embodiment;

FIG. 2 is a cross-sectional view illustrating an exemplary structure ofa phase modulator adoptable in the phase modulation active deviceillustrated in FIG. 1 ;

FIG. 3 is a cross-sectional view illustrating another exemplarystructure of a phase modulator adoptable in the phase modulation activedevice illustrated in FIG. 1 ;

FIG. 4 is a flowchart schematically illustrating a method of driving aphase modulation active device according to an example embodiment;

FIG. 5 illustrates a phase profile that sets a phase value of eachchannel to drive a phase modulation active device as a beam steeringdevice;

FIG. 6 is a conceptual graph for describing a phase limit;

FIG. 7 illustrates a phase profile implemented in a phase modulationactive device according to a comparison example;

FIG. 8 is a graph showing an example in which a target phase value forlimit channels is reset based on a method of driving a phase modulationactive device according to an example embodiment;

FIG. 9 is a graph showing another example in which a target phase valuefor limit channels is reset based on a method of driving a phasemodulation active device according to an example embodiment;

FIG. 10 is a graph showing an intensity distribution with respect to anangle for light modulated by a phase modulation active device accordingto an example embodiment;

FIG. 11 is a graph showing an intensity distribution with respect to anangle for light modulated by a phase modulation active device accordingto a comparative example;

FIG. 12 is a graph for comparing a phase profile of an embodiment and aphase profile of a comparative example with an ideal case to implementbeam steering;

FIG. 13 is a graph showing a ratio of a main peak to a side lobe forlight modulated by phase modulation active devices according to anembodiment and a comparative example with respect to a phase limitvalue;

FIG. 14 is a graph showing a relative ratio of a main peak of lightmodulated by phase modulation active devices according to an embodimentto a comparative example with respect to a phase limit value; and

FIG. 15 is a block diagram schematically illustrating a structure of alidar device according to an example embodiment.

DETAILED DESCRIPTION

Reference will now be made in detail to example embodiments, which areillustrated in the accompanying drawings, wherein like referencenumerals refer to like elements throughout. In this regard, the presentexample embodiments may have different forms and should not be construedas being limited to the descriptions set forth herein. Accordingly, theexample embodiments are described below, by referring to the figures, toexplain aspects. As used herein, the term “and/or” includes any and allcombinations of one or more of the associated listed items. Expressionssuch as “at least one of,” when preceding a list of elements, modify theentire list of elements and do not modify the individual elements of thelist.

Hereinafter, example embodiments of the present disclosure will bedescribed in detail with reference to the accompanying drawings.Throughout the drawings, like reference numerals refer to like elements,and each element may be exaggerated in size for clarity and convenienceof a description. Meanwhile, the following example embodiments aremerely illustrative, and various modifications may be possible from theexample embodiments.

An expression such as “above” or “on” may include not only the meaningof “immediately on and in contact with,” but also the meaning of “onwithout making contact.”

The singular forms are intended to include the plural forms as well, andvice versa, unless the context clearly indicates otherwise. If it isassumed that a certain part includes a certain component, the term‘including’ means that a corresponding component may further includeother components unless a specific meaning opposed to the correspondingcomponent is written.

The use of “the” and other demonstratives similar thereto may correspondto both a singular form and a plural form.

Unless the order of operations of a method is explicitly mentioned ordescribed otherwise, the operations may be performed in any order. Theorder of the operations is not limited to the order the operations arementioned. The use of all examples or exemplary terms (e.g., “etc.,”“and (or) the like,” and “and so forth”) is merely intended to describedtechnical aspects in detail, and the scope is not necessarily limited bythe examples or exemplary terms unless defined by the claims.

FIG. 1 is a block diagram schematically illustrating a structure of aphase modulation active device 1000 according to an example embodiment.FIGS. 2 and 3 illustrate a detailed structure of phase modulators 101and 102, respectively, which are adoptable in the phase modulationactive device 1000.

The phase modulation active device 1000 may include a phase modulator100 including a plurality of channels CH_1 through CH_N for modulating aphase of incident light, a signal input unit 200 for applying an inputsignal (e.g., control signal) for phase modulation to each of theplurality of channels CH_1 through CH_N, and a controller 300 forcontrolling the signal input unit 200.

The phase modulator 100 may include the plurality of channels CH_1through CH_N to independently modulate a phase of incident light L_(i).The phase modulator 100 may include an active layer having opticalproperties that change with an applied signal and a plurality of nanostructures arranged adjacent to or over the active layer, wherein eachof the plurality of nano structures may form the plurality of channelsCH_1 through CH_N. A detailed exemplary structure of the phase modulator100 may be described with reference to FIGS. 2 and 3 . Each of theplurality of channels CH_1 through CH_N may modulate a phase of theincident light L_(i) according to a signal applied thereto from thesignal input unit 200. The input signal from the signal input unit 200may be determined according to a detailed structure of the phasemodulator 100, e.g., materials of the active layer and the nanostructure adopted in the phase modulator 100. If the phase modulator 100adopts a material having optical properties that change with an electricsignal, the signal input unit 200 may be configured to apply an electricsignal, e.g., a voltage signal, to the phase modulator 100. Byappropriately controlling regularity for modulating a phase in each ofthe plurality of channels CH_1 through CH_N of the phase modulator 100,the incident light L_(i) may be output as modulated light L_(m) invarious forms, and the phase modulator 100 may perform, for example,beam steering, focusing, defocusing, beam shaping, beam splitting, orthe like, with respect to the incident light L_(i).

The controller 300 may control the signal input unit 200 such that eachof the plurality of channels CH_1 through CH_N is independently suitablycontrolled with respect to a wavelength of the incident light L_(i) tobe modulated and a desired modulation type. The controller 300 mayinclude circuitry that generates and/or adjust an electric signal. Forexample, the controller 300 may be a processor, a central processingunit (CPU), a system-on-chip (SoC), an application-specific integratedcircuit (ASIC), etc. The phase modulation active device 1000 may alsoinclude computer-readable storage device (e.g., volatile or non-volatilememory) for storing instructions which, when executed by the controller300, cause the controller 300 to perform various operations as disclosedherein, e.g., control the input signal emitting from the signal inputunit 200.

FIGS. 2 and 3 illustrate a detailed structure of the phase modulators101 and 102 adoptable in the phase modulation active device 1000. Inother words, either one or both of the phase modulators 101 and 102 maybe used in the phase modulation active device 1000 as one or morechannels of the phase modulator 100.

Referring to FIG. 2 , the phase modulator 101 may include an activelayer 20, a nano array layer 50 in which a conductive nano structure 52is arrayed, and an electrode layer 10 for applying a signal to theactive layer 20. The active layer 20 may include a material havingoptical properties that change with signal application. The active layer20 may include, for example, a material having a dielectric constantthat changes with an electric field. The nano array layer 50 may includea plurality of nano structures 52, although in the drawings, one nanostructure 52 forming one channel is illustrated as an example. Aninsulating layer 30 may be further disposed between the nano array layer50 and the active layer 20. A voltage 70 may be applied between theelectrode layer 10 and the nano array layer 50.

The nano structure 52 may have a shape dimension of a sub-wavelength.Herein, the sub-wavelength means dimensions smaller than an operationwavelength of the phase modulator 100, i.e., wavelength of the incidentlight L_(i) to be modulated. One or more dimensions that form the shapeof the nano structure 52, e.g., at least one of a thickness, a width,and a length, may be a sub-wavelength dimension.

The conductive material adopted in the nano structure 52 may include ahigh-conductivity metallic material in which surface plasmon excitationmay occur. For example, at least any one selected from among copper(Cu), aluminum (Al), nickel (Ni), iron (Fe), cobalt (Co), zinc (Zn),titanium (Ti), ruthenium (Ru), rhodium (Rh), palladium (Pd), platinum(Pt), silver (Ag), osmium (Os), iridium (Ir), and gold (Au) may beadopted, or an alloy including any one of these elements may be adopted.A two-dimensional (2D) material having superior conductivity, such asgraphene or conductive oxide, may be used.

The active layer 20 may include a material having opticalcharacteristics that change with an external signal. The external signalmay be an electric signal. The active layer 20 may include transparentconductive oxide (TCO) such as indium tin oxide (ITO), indium zinc oxide(IZO), aluminum zinc oxide (AZO), gallium zinc oxide (GZO), or the like.Transition metal nitride such as TiN, ZrN, HfN, or TaN may also be usedfor the active layer 20. Moreover, an electro-optic material having aneffective dielectricity that changes with application of an electricsignal, e.g., LiNbO3, LiTaO3, potassium tantalate niobate (KTN), leadzirconate titanate (PZT), etc., may be used, and various polymermaterials having electro-optic characteristics may be used.

The electrode layer 10 may be formed using various materials havingconductivity. The electrode layer 10 may include at least any oneselected from among Cu, Al, Ni, Fe, Co, Zn, Ti, Ru, Rh, Pd, Pt, Ag, Os,Ir, and Au. If the electrode layer 10 includes a metallic material, theelectrode layer 10 may function as a reflective layer for reflectinglight as well as to apply a voltage. The electrode layer 10 may includetransparent conductive oxide (TCO) such as ITO, IZO, AZO, GZO, or thelike.

The nano structure 52 may modulate a phase of light having a particularwavelength using surface plasmon resonance occurring in a boundarybetween the metallic material and a dielectric material, and the outputphase value is related to a detailed shape of the nano structure 52. Theoutput phase value may be adjusted by a change of the optical propertiesof the active layer 20 due to a voltage applied between the nanostructure 52 and the electrode layer 10.

Referring to FIG. 3 , the phase modulator 102 may include an activelayer 22, a nano array layer 60 in which a dielectric nano structure 62is arrayed, and an electrode layer 10 for applying a signal to theactive layer 22. The active layer 22 may include a material havingoptical properties that change with signal application, e.g., a materialhaving a dielectric constant that changes with an electric field. Thenano array layer 60 may include a plurality of nano structures 62,although in the drawings, one nano structure 62 forming one channel isillustrated as an example. A conductive layer 40 may be further disposedbetween the nano array layer 60 and the active layer 22. The voltage 70may be applied between the electrode layer 10 and the conductive layer40.

The active layer 22 may include an electro-optic material having arefractive index that changes according to an effective dielectricconstant that changes with application of an electric signal. As theelectro-optic material, LiNbO3, LiTaO3, KTN, PZT, etc., may be used, andvarious polymer materials having electro-optic characteristics may alsobe used.

The electrode layer 10 may be formed using various materials havingconductivity. The electrode layer 10 may include at least any oneselected from among Cu, Al, Ni, Fe, Co, Zn, Ti, Ru, Rh, Pd, Pt, Ag, Os,Ir, and Au. If the electrode layer 10 includes a metallic material, theelectrode layer 10 may function as a reflective layer for reflectinglight as well as to apply a voltage. The electrode layer 10 may includetransparent conductive oxide (TCO) such as ITO, IZO, AZO, GZO, or thelike.

The nano structure 62 may have a shape dimension of a sub-wavelength.The nano structure 62 may include a dielectric material to modulate aphase of light having a particular wavelength by using Mie resonancecaused by a displacement current. To this end, the nano structure 62 mayinclude a dielectric material having a refractive index higher than thatof the active layer 22, for example, a material having a refractiveindex higher than the highest value in a range in which the refractiveindex of the active layer 22 changes by application of a voltage. Thephase value output by the nano structure 62 may be related to a detailedstructure of the nano structure 62. The output phase value from the nanostructure 62 may be adjusted by a change of the optical properties ofthe active layer 10 due to a voltage applied between the conductivelayer 40 and the electrode layer 10.

FIGS. 2 and 3 illustrate exemplary structures in the phase modulators101 and 102, respectively, and the phase modulator 100 of the phasemodulation active device 1000 illustrated in FIG. 1 is not limited tothe illustrated structures, and a modified form thereof may be adoptedin the phase modulation active device 1000.

To control the phase modulation active device 1000, a phase modulationrange implemented by each channel of the phase modulator 100 needs tocover 0° through 360°. However, a phase modulation value may notincrease beyond a specific limit even if an input signal is increased,which is referred to as phase limit. The phase limit may have a valueless than 360°, for example, 210°, 300°, 330°, etc., and if the phasemodulator 100 shows the phase limit, a target phase may not be achievedin a channel needing phase modulation beyond the phase limit and up to360°, resulting in degraded optical modulation performance.

For example, if the phase modulator 100 implements beam steering, aplurality of channels adjacent to each other show a linearly increasingphase, a phase difference between adjacent channels is Δφ, and a channelwidth is d, then light having a wavelength λ is steered in a directionat an angle θ from the light's original path, where the angle θ isdefined as follows:

${\sin\theta} = {\frac{\Delta\phi}{2\;\pi}\frac{\lambda}{d}}$

However, if the phase value of the channels fails to reach 360° due tothe phase limit, a part of the incident light L_(i) is steered in adirection other than θ. That is, a distribution of the modulated lightL_(m) may exhibit a peak in a position other than a desired angle θ.Then, a peak magnitude at the desired angle θ may be correlativelyreduced. Due to this phenomenon, signal-to-noise ratio (SNR) may belowered and luminance efficiency may also be reduced.

The phase modulation active device 1000 according to the exampleembodiment may reduce or minimize performance degradation of the phasemodulation active device 1000 due to phase limit by adjusting a targetphase value for a channel showing phase limit among the plurality ofchannels CH_1 through CH_N of the phase modulator 100. To this end, thecontroller 300 may control the signal input unit such that a targetphase value for at least a part of a channel showing phase limit amongthe plurality of channels is less than a phase limit value. The adjustedtarget phase value may be, for example, a minimum value among phasemodulation values that may be implemented by the phase modulator 100according to an input signal.

Hereinafter, referring to FIGS. 4 through 9 , a method of driving aphase modulation active device according to an example embodiment willbe described.

FIG. 4 is a flowchart schematically illustrating a method of driving aphase modulation active device according to an example embodiment.

Referring to FIG. 4 , for the phase modulation active device, a phaseprofile indicating a channel-specific target phase modulation value(also referred to a phase modulation target value or a target phasevalue) may be configured in operation S310.

As stated above, optical modulation characteristics of the phasemodulation active device may be controlled according to rules ofchannel-specific phase modulation, such that the phase modulationprofile is configured suitably for optical performance to beimplemented.

FIG. 5 illustrates a phase profile that sets a phase value of eachchannel to drive (e.g., operate) a phase modulation active device as abeam steering device.

The illustrated phase profile shows an example designed such that lightincident to the phase modulation active device 1000 is directed toward asteering angle θ_(T) by the phase modulation active device 1000. Ahorizontal axis of a graph plots a channel ID. In the illustrated phaseprofile, a phase value is 0° in channel 1, and a phase value of eachchannel linearly increases up to 360° in a direction toward an adjacentchannel, and then goes back to 0° and increases up to 360° again.

Next, a phase limit value φ_(lim) of the phase modulation active device1000 may be set in operation S320. To set the phase limit value φ_(lim),the change of a phase modulation value according to the change of anapplied voltage may be analyzed. The analysis of the change may beperformed with respect to one channel of the phase modulation activedevice 1000.

FIG. 6 is a conceptual graph for describing a phase limit.

By analyzing a tendency of the change of the phase modulation value withrespect to the change of the applied voltage (e.g., correlation betweenthe phase modulation value and the applied voltage), an appliedvoltage-versus-phase graph may be obtained. Referring to the graph, asan applied voltage increases, a phase output value may likewiseincrease, but may be saturated at the phase limit value φ_(lim), andonce being saturated, the phase output value may not increase any longereven if the applied voltage increases.

From the graph of FIG. 6 , the phase limit value φ_(lim) and an appliedvoltage Vs for reaching the phase limit value φ_(lim) may be set, and aminimum value φ_(min) and a maximum value φ_(max) of phase modulation tobe implemented by the phase modulation active device and appliedvoltages V₀ and V_(m) for the minimum value φ_(min) and the maximumvalue φ_(max), respectively, may also be set.

The minimum value φ_(min) may be 0, without being limited thereto.

The maximum value φ_(max) may be set to the same value as the phaselimit value φ_(lim) or to a value less than the phase limit valueφ_(lim), for example, a specific percentage or ratio (e.g., 90%, 95%) orhigher of the phase limit value φ_(lim). The graph includes a range inwhich a gradient of a phase increase with respect to an applied voltageincrease is significantly low as a region for implementing a phase veryclose to the phase limit value φ_(lim), and by setting the maximum valueφ_(max) in the range, an efficient applied voltage may be set. The setmaximum value φ_(max) and minimum value φ_(min) may be used to modify atarget phase value in the next operation S330.

FIG. 7 illustrates a phase profile implemented in a phase modulationactive device according to a comparison example.

The phase profile illustrated in FIG. 7 is implemented in the phasemodulation active device with a phase limit when a voltage is applied toeach channel of the phase modulation active device to implement thephase profile of FIG. 5. Herein, a comparative example means a casewhere the driving method according to an example embodiment is notapplied.

The graph also shows, with a dotted line, a case where the target phaseprofile set in FIG. 5 is ideally implemented. In the target phaseprofile, channels A needing the phase limit value φ_(lim) or higher(e.g., channels having phase modulation targets that exceed the phaselimit value φ_(lim)) are referred to as limit channels A. In the limitchannels A, a value higher than the phase limit value φ_(lim) may not besubstantially implemented. That is, the limit channels A may exhibit thephase limit value φ_(lim), instead of their target phase values.

In the driving method according to an example embodiment, for the limitchannels A, the target phase value may be modified in operation S330,and the phase modulation active device may be driven according to themodified phase profile in operation S340.

The phase of the limit channels A may be reset to a value lower than thetarget phase values set in the target phase profile. For at least someof the limit channels A, modification to a lower target phase value maybe performed, and the modified value may be the minimum value φ_(min)that may be implemented by the phase modulation active device.

FIG. 8 is a graph showing an example in which a target phase value forthe limit channels A is reset based on a method of driving a phasemodulation active device according to an example embodiment.

Referring to FIG. 8 , a target phase value for the limit channels A maybe modified to the minimum value φ_(min) that is set in FIG. 6 . Inother words, phases of the channels A needing (e.g., ideally targetedfor) the phase limit value φ_(lim) or higher is reset to the minimumvalue φ_(min). In the graph, the vertical line on the right-hand sideindicates an applied voltage, and the applied voltage V₀ implementingthe minimum value φ_(min) may be determined from the graph of FIG. 6 .

Although the phase is reset to the minimum value φ_(min) for all thelimit channels A in FIG. 8 , the phases may be set to the minimum valueφ_(min) for only some of the limit channels A. For example, phases ofsome of the limit channels A may be reset to the minimum value φ_(min),and phases of others may be reset to the maximum value φ_(max).

FIG. 9 is a graph showing another example in which a target phase valuefor the limit channels A is reset based on a method of driving a phasemodulation active device according to an example embodiment.

Referring to FIG. 9 , a portion (e.g., one half) of the limit channels Amay be reset to the maximum value φ_(max), and another portion (e.g.,the other half) may be reset to the minimum value φ_(min). To drive(e.g., operate) the phase modulation active device in this way, an inputsignal V_(m) for implementing the maximum value φ_(max) may be appliedto one half of the limit channels A, whereas an input signal V₀ forimplementing φ_(min) may be applied to the other half. As shown in FIG.9 , for a half of the limit channels A having a relatively largedifference (e.g., a difference of more than a predetermined thresholddifference value) between a target phase value and the phase limit valueφ_(lim) (e.g., when the target phase value is higher than apredetermined threshold phase value), the phase may be reset to theminimum value φ_(min), and for the other half having a relative smalldifference (e.g., a difference of less than the predetermined thresholddifference value) between the target phase value and the phase limitvalue φ_(lim) (e.g., when the target phase value is lower than apredetermined threshold phase value), the phase may be reset to themaximum value φ_(max). The maximum value φ_(max) may be equal to or lessthan the phase limit φ_(lim), as mentioned with reference to FIG. 6 .

FIG. 10 is a graph showing an intensity distribution with respect to anangle for light modulated by a phase modulation active device accordingto an example embodiment.

In FIG. 10 , the phase modulation active device is driven based on aphase profile according to an example embodiment reset as shown in FIG.9 . Referring to the graph, at a target steering angle θ_(T), maximumintensity is shown in arbitrary units (AU), and at some other angularpositions, smaller peaks are shown. In the graph, a peak at the intendedangle θ_(T) is referred to as a main peak, and other peaks are referredto as side lobes.

FIG. 11 is a graph showing an intensity distribution with respect to anangle for light modulated by a phase modulation active device accordingto a comparative example.

FIG. 11 illustrates modulated light when the phase modulation activedevice is driven according to the phase profile corresponding to thecomparative example shown in FIG. 7 , that is, when the target phasevalues for the limit channels A are not reset. Also in the graph of FIG.11 , the maximum intensity is shown at the target steering angle θ_(T),and a plurality of side lobes may be seen.

In the graphs of FIGS. 10 and 11 , the side lobes may be seen becausethe phase profile as shown in FIG. 5 may not be implemented due to thephase limit. Comparing the graph of FIG. 10 with the graph of FIG. 11 ,the magnitudes of the side lobes in the graph of FIG. 10 according tothe driving method of the example embodiment are smaller than those ofthe side lobes in the graph of FIG. 11 according the comparativeexample. The magnitude of the main peak is also higher in FIG. 10 thanin FIG. 11 . This effect is obtained by resetting the phase value forthe limit channels A.

When the driving method according to an example embodiment is applied, ahigher main peak and lower side lobes are shown than with thecomparative example where the driving method according to an exampleembodiment is not applied, as can be predicted from the graph of FIG. 12.

FIG. 12 is a graph for comparing a phase profile of an exampleembodiment and a phase profile of a comparative example with an idealcase to implement beam steering.

In the graph, a vertical axis plots target phases to be implemented byrespective channels, in an manner by which the phase values wrap aroundthe angle 360°. That is, phases of a series of channels that follow thechannels with their phases linearly increasing from 0° to 360° areindicated as ranging from 360° to 720°.

Referring to the graph, the degree to which a given phase valueimplemented for one of the limit channels A deviates from the targetphase value is much lower in the example embodiment than in thecomparative example.

FIG. 13 is a graph showing a ratio of a main peak to a side lobe forlight modulated by phase modulation active devices according to anexample embodiment and a comparative example with respect to a phaselimit value.

In FIG. 13 , a horizontal axis plots a phase limit value φ_(lim), and avertical axis plots a ratio of a magnitude of a main peak relative to amagnitude of a side lobe. As the phase limit value φ_(lim) moves toward360°, a performance difference between the comparative example and theexample embodiment becomes smaller. As the phase limit value φ_(lim)moves away from 360°, a performance difference between the comparativeexample and the example embodiment becomes larger. Once the phase limitvalue φ_(lim) is less than about 330°, then the performance differencebetween the comparative example and the example embodiment becomessignificant, resetting phase values for limit channels based on thedriving method according to the example embodiment help obtain desiredoptical performance.

FIG. 14 is a graph showing a relative ratio of a main peak of lightmodulated by phase modulation active devices according to an exampleembodiment to a comparative example with respect to a phase limit value.

In FIG. 14 , a horizontal axis plots a phase limit value φ_(lim), and avertical axis plots a relative magnitude of a main peak (e.g., relativeto a magnitude of a side lobe). As the phase limit value φ_(lim) movesaway from 360°, a performance difference between the comparative exampleand the example embodiment becomes larger. As the phase limit valueφ_(lim) becomes less than 300°, a performance difference between thecomparative example and the embodiment becomes significantly larger.

From both the graph of FIG. 13 and the graph of FIG. 14 , it can be seenthat for all phase limit values φ_(lim), the optical performance of theexample embodiment is better than that of the comparative example, andin addition, the performance difference therebetween becomes larger asthe phase limit value φlim becomes smaller. The graph of FIG. 13 mayshow an SNR-related value, and the graph of FIG. 14 may show a luminanceefficiency-related value, and these two factors may be important tooptical modulation performance. In this regard, when a channel showingphase limit at about 330° or lower is used for a phase modulation activedevice, optical modulation performance may be effectively improved byusing the driving method according to an example embodiment.

The phase modulation active device 1000 may have various opticalcapabilities by appropriately setting a phase modulation rule in eachchannel, thus being applicable to various optical devices.

The phase modulation active device 1000 may be used for a refractiveoptical lens that may be focused or defocused, and may be applied tovarious optical systems using such an optical lens. Moreover, withactive performance adjustment, the phase modulation active device 1000may perform a function such as variable focusing.

The phase modulation active device 1000 may be applied as a beamsplitter that splits incident light in various directions, as a beamshaper that performs beam shaping, or as a beam steering device thatsteers light in a desired direction. The phase modulation active device1000 may be used in various optical systems using a beam splitter, abeam former, a beam steering device, or the like. Moreover, with activeperformance adjustment, e.g., steering direction adjustment, the phasemodulation active device 1000 may perform a function such as beamscanning.

FIG. 15 is a block diagram schematically illustrating a structure of alidar device 2000 according to an example embodiment.

The lidar device 2000 may include a light source unit 1200 thatirradiates light, the phase modulation active device 1000 that steersthe light irradiated from the light source unit 120 toward an objectOBJ, and a sensor unit 1400 that senses light reflected from the objectOBJ.

The light source unit 1200 may irradiate light to be used for theanalysis of a location and a shape of the object OBJ. The light sourceunit 1200 may include a light source that generates and irradiates lighthaving a specific wavelength. The light source unit 1200 may include alight source such as a laser diode (LD), a light emitting diode (LED), asuper luminescent diode (SLD), or the like, which generates andirradiates light having a wavelength band suitable for the analysis ofthe position and the shape of the object OBJ, e.g., light having aninfrared wavelength. The light source unit 1200 may generate andirradiate light in a plurality of different wavelength bands. The lightsource unit 1200 may generate and irradiate pulse light or continuouslight.

The phase modulation active device 1000 may include the phase modulator100 including a plurality of channels for independently modulating aphase of incident light, the signal input unit 200 for applying an inputsignal for phase modulation to each of the plurality of channels, andthe controller 300 for controlling the signal input unit 200. The phasemodulator 100 may have the same structure as one or both of theabove-described phase modulators 101 and 102.

Between the light source unit 1200 and the phase modulation activedevice 1000 and/or between the phase modulation active device 1000 andthe object OBJ, other optical members, for example, members foradjusting a path of light irradiated from the light source 1200,splitting a wavelength of the irradiated light, or performing additionalmodulation, may be further disposed.

The controller 300 may set a target phase value for each of theplurality of channels CH_1 through CH_N to cause the phase activemodulation device 1000 to perform beam steering, and controls the signalinput unit 200 to apply an input signal for this end. The controller 300may control the signal input unit 200 to apply an input signal forlowering a target phase value for at least some of the plurality ofchannels, which exhibit a phase limit, as described above in relation tothe driving method. The controller 300 may also control the signal inputunit 200 to sequentially adjust the steering direction of the phasemodulation active device 1000 over a period of time, thereby to scan theobject OBJ with sweeping incident light. The steering angle of the phasemodulation active device 1000 may cover a range from θ_(T1) to θ_(T2),and during scanning in the range, an optical signal sensed by the sensorunit 1400 may be used to analyze the presence, location, and shape ofthe object OBJ.

The sensor unit 1400 may include an array of a plurality of sensors foroptical detection that senses light reflected from the object OBJ. Thesensor unit 1400 may also include arrays of sensors capable of sensinglight having a plurality of different wavelengths.

The lidar device 2000 may further include a signal processor 1600. Thesignal processor 1600 may perform a predetermined operation, e.g., anoperation for measuring a time of flight, from the optical signaldetected by the sensor unit 1400 and performs three-dimensional (3D)shape identification based on the operation. The signal processor 1600may use various operation methods. For example, according to a directtime measurement method, pulse light is irradiated to the object OBJ,the time of arrival of the light after being reflected from the objectOBJ is measured by using a timer, and then calculating a distance iscalculated. According to a correlation method, the pulse light isirradiated to the object OBJ and the distance is measured from abrightness of the light reflected from the object OBJ. According to aphase delay measurement method, light of a continuous wave, such as asine wave is irradiated to the object OBJ, a phase difference of thelight reflected from the object OBJ is sensed, and then the phasedifference is converted into the distance. The signal processor 1600 mayinclude a memory (e.g., a computer-readable storage medium) in which aprogram (e.g., instructions) necessary for the operation and other datamay be stored. The signal processor 1600 may be implemented with aprocessor, a CPU, a SoC, an ASIC, etc.

The signal processor 1600 may transmit an operation result, that is,information about the shape and location of the object OBJ, to anotherunit. For example, the information may be transmitted to a automotivedriving controller or an alert system, etc., of a self-driving device(e.g., vehicle) employing the lidar device 2000.

The lidar device 2000 may be used as a sensor for obtaining 3Dinformation about a forward object in real time, thus being applicableto a self-driving device, e.g., a unmanned vehicle, a self-drivingvehicle, a robot, a drone, etc.

The lidar device 2000 may also be applied to a vehicle black box (e.g.,dashboard camera) or the like as well as the self-driving device, so asto identify forward or rearward obstacles at night or in the dark whenobjects are difficult to identify with a conventional image sensoralone.

According to the above-described method of driving the phase modulationactive device, improved optical modulation is possible by modifying atarget phase value for channels that exhibit a phase limit.

The above-described phase modulation active device may reduce orminimize performance degradation caused by a phase limit even when it isnecessary to include channels that exhibit a phase limit to improveoptical modulation performance.

The phase modulation active device also has good optical modulationperformance that is actively controlled according to an applied voltage,thus being applicable to various optical devices.

So far, example embodiments have been described and illustrated in theattached drawings to help understanding of the present disclosure.However, it should be understood that these example embodiments areintended to merely describe the present disclosure and do not limit thepresent disclosure. It also should be understood that the presentdisclosure is not limited to the illustrated and provided description.Therefore, various modifications may be made by those of ordinary skillin the art.

It should be understood that example embodiments described herein shouldbe considered in a descriptive sense only and not for purposes oflimitation. Descriptions of features or aspects within each exampleembodiment should typically be considered as available for other similarfeatures or aspects in other example embodiments.

While one or more example embodiments have been described with referenceto the figures, it will be understood by those of ordinary skill in theart that various changes in form and details may be made therein withoutdeparting from the spirit and scope as defined by the following claims.

What is claimed is:
 1. A phase modulation active device comprising: aphase modulator comprising a plurality of channels, each channel of theplurality of channels configured to modulate a phase of incident lightindependently from other channels of the plurality of channels, based ona target phase modulation value; a signal input unit configured to applyan input signal for phase modulation to the each channel of theplurality of channels; and a controller configured to control the signalinput unit to apply the input signal, which implements a phasemodulation value less than the target phase modulation value of achannel, to at least one channel included a channel group includingchannel of which target phase modulation value is equal to or largerthan a predetermined phase value, among the plurality of channels, withrespect to a portion of channels of the channel group, the input signalbeing to implement a first phase modulation value less than thepredetermined phase modulation value, with respect to a remainingportion of channels of the channel group, the input signal being toimplement a second phase modulation value less than the predeterminedphase modulation value and different to the first phase modulationvalue.
 2. The phase modulation active device of claim 1, wherein thefirst phase modulation value is a minimum value among phase modulationvalues that are implemented by the phase modulator.
 3. The phasemodulation active device of claim 1, wherein the predetermined phasemodulation value is less than 330°.
 4. The phase modulation activedevice of claim 1, wherein the second phase modulation value is amaximum value among the phase modulation values that are implemented bythe phase modulator.
 5. The phase modulation active device of claim 1,wherein the portion of channels of the channel group is a half of thechannel group, and the remaining portion of channels of the channelgroup is another half of the channel group.
 6. The phase modulationactive device of claim 1, wherein the phase modulator is configured tomodulate the phase of the incident light according to an appliedvoltage, and the portion of the channel group includes channels havingtarget phase values exceeding a predetermined threshold value, a firstvoltage value implementing the first phase modulation value is appliedto the portion of the channel group, and a second voltage valueimplementing the second phase modulation value is applied to theremaining portion of the channel group.
 7. The phase modulation activedevice of claim 1, wherein the phase modulator comprises: an activelayer having optical characteristics that change with an electricsignal; a nano array layer comprising a plurality of nano structuresarranged over the active layer; and an electrode layer configured toapply a signal to the active layer.
 8. The phase modulation activedevice of claim 7, wherein each nano structure of the plurality of nanostructures has a shape dimension that is smaller than a wavelength ofthe incident light.
 9. The phase modulation active device of claim 1,wherein the signal input unit is further configured to cause the phasemodulator to perform at least one of beam steering, focusing,defocusing, beam shaping, or beam splitting.
 10. An optical devicecomprising the phase modulation active device of claim
 1. 11. A lidardevice comprising: a light source unit; a phase modulation active deviceof claim 1 configured to steer light from the light source unit towardan object; and a sensor unit configured to receive the light that issteered by the phase modulation active device, irradiated to the object,and reflected from the object.
 12. The lidar device of claim 11, whereinthe controller is further configured to control the signal input unit tosequentially adjust a steering direction of the phase modulation activedevice to scan the object.
 13. A method of driving a phase modulationactive device, the phase modulation device comprising a phase modulatorincluding a plurality of channels, each channel of the plurality ofchannels configured to modulate a phase of incident light independentlyfrom other channels of the plurality of channels, based on a targetphase modulation value, the method comprising: applying an input signalwhich implements a phase modulation value less than the target phasemodulation value of a channel, to at least one channel included achannel group including channel of which target phase modulation valueis equal to or larger than a predetermined phase value, among theplurality of channels, with respect to a portion of channels of thechannel group, the input signal being to implement a first phasemodulation value less than the predetermined phase modulation value,with respect to a remaining portion of channels of the channel group,the input signal being to implement a second phase modulation value lessthan the predetermined phase modulation value and different to the firstphase modulation value.
 14. The method of claim 13, wherein the firstphase modulation value is a minimum value among phase modulation valuesthat are implemented by the phase modulator.
 15. The method of claim 13,wherein the predetermined phase modulation value is less than 330°. 16.The method of claim 13, wherein the second phase modulation value is amaximum value among the phase modulation values that are implemented bythe phase modulator.
 17. The method of claim 13, wherein the portion ofchannels of the channel group is a half of the channel group, and theremaining portion of channels of the channel group is another half ofthe channel group.
 18. The method of claim 13, wherein the phasemodulator is configured to modulate the phase of the incident lightaccording to an applied voltage, and the portion of the channel groupincludes channels having target phase values exceeding a predeterminedthreshold value, a first voltage value implementing the first phasemodulation value is applied to the portion of the channel group, and asecond voltage value implementing the second phase modulation value isapplied to the remaining portion of the channel group.